Fluid control devices are used in variety of systems (e.g., natural gas delivery systems, chemical treatment systems, etc.) to control the flow of a fluid therethrough. Fluid control devices encompass various categories of equipment including control valves and regulators. In general, fluid control devices have a fluid flow path and a control member for adjusting a dimension of the fluid flow path.
FIG. 1 depicts a known regulator 10 including a valve body 12 and an actuator 14. The valve body 12 includes an inlet 13 and an outlet 16 with a flow path 18 extending therebetween. A portion of the flow path 18 is defined by a throat 20, and a valve seat ring 22 is disposed in the throat 20. The actuator 14 includes an actuator casing 24 having an upper portion 26 removably attached to a lower portion 28. The actuator 14 also includes a diaphragm 30 disposed between and separating the upper and lower portions 26 and 28 of the actuator casing 24, and a control member 32 disposed in the flow path 16. The lower portion 28 of the of the actuator casing 24 is in fluid communication with a downstream control line (not illustrated). Accordingly, a downstream pressure is supplied to the lower portion of the actuator casing 28 and exerts a force against the diaphragm 30.
The control member 32 is configured to reciprocate between an open position and a closed position in response to changes in pressure across the diaphragm 30. In the open position (not illustrated), the control member 32 is spaced apart from the valve seat ring 22, thereby allowing fluid to flow through the throat 20. In the closed position (illustrated in FIG. 1), the control member 32 sealingly engages the valve seat ring 22 to prevent or inhibit fluid from flowing through the throat 20.
The regulator assembly 10 includes a coil spring 34 that biases the control member 32 to the open position. When the outlet pressure of the valve body 12 is low, the coil spring 34 moves the control member 32 to the open position. By contrast, when the outlet pressure of the valve body 12 is high, the pressure exerted against the diaphragm 30 overcomes the biasing force of the coil spring 34, thereby moving the control member 32 to the closed position. Due to this arrangement of the coil spring 34, the regulator 10 is generally classified as a “fail-open” regulator. Other regulators are configured as “fail-closed” regulators, where the spring that biases the control member to the closed position.
As depicted in FIG. 1, conventional regulators typically employ a valve stem 40 to connect the coil spring 34 to the control member 32. A lower end 42 of the valve stem 40 possesses an annular protrusion 44 and a threaded end portion 46. During assembly, the threaded end portion 46 is inserted through a through-hole in the control member 32 such that the control member 32 is positioned between the annular protrusion 44 and the threaded end portion 46. Subsequently, a retaining nut 48 is rotated about the threaded end portion 46 and threadably advanced into contact with a bottom surface 50 of the control member 32. The control member 32 is thereby secured between the annular protrusion 44 and the retaining nut 48.
Conventional control members typically have a bottom surface that is planar across its entire width. Therefore, as depicted in FIG. 2, the retaining nut 48 protrudes outwardly from the bottom surface 50 of the control member 32, and imparts the bottom of the control member 32 with a bulbous profile. Consequently, fluid must flow around the retaining nut 48 during operation. As the control member 32 changes position during operation, the path of the fluid around the retaining nut 48 also changes. As a result, in certain flow conditions, the fluid pressure exerted against the bottom surface 50 of the control member 32 may be less than the fluid pressure exerted against a top surface 52 of the control member 32. In some cases, this pressure differential may cause the control member 32 to settle into a pattern of high frequency oscillations, which in turn, may result in an unstable output pressure of the regulator 10. This phenomenon is more likely to occur in low flow conditions, where any change in the position of the control member 32 can have a large effect on the force balance.
The present disclosure sets forth fluid control devices and methods of assembling such devices embodying advantageous alternatives to existing fluid control devices and existing methods of assembly, and that may address one or more of the challenges or needs mentioned above, as well as provide other benefits and advantages.